This invention is related to devices or robots used for practice in sports such as baseball, tennis and table tennis. More specifically, it relates to table tennis robots that employ motor-rotated wheels to engage a ball, thereby providing the thrust required for projecting the ball. The invention is intended to be adapted as the throwing mechanism or head for a table tennis robot.
In general, robots employ rotating wheels to engage the ball while simultaneously pressing it against another rotating wheel or fixed surface, thereby rolling and projecting the ball into open space. A single rotating wheel may be used, in which case, the ejected ball always carries spin, or, two rotating wheels may be employed, in which case, the ball can be ejected with spins or no spin.
When two wheels are used, a ball without spin is possible when both wheels rotate in opposite directions at the same speed and engage the ball between their peripheries. If only one wheel rotates to throw the ball, then clockwise spin for example, is on the ejected ball. If only the other wheel rotates then counterclockwise spin is produced. The magnitude of the spin on an ejected ball is proportional to the speed at which the ball is ejected.
The mass of the wheels and moving parts of the motors in a ball-throwing mechanism, limits the rate at which the motors can speed up or slow down. This is due to the inertia of these components. In practice, motors and wheels found suitable for throwing balls, require several seconds to rotate from zero RPM to their maximum speed. Conversely, they require approximately the same time to return to zero RPM. Inertia is therefore a limiting factor when the motors must be sped up or slowed down.
When experienced players play table tennis, they often execute two or more strokes each second. Moreover, they can change the magnitude and direction of rotation of the ball on successive strokes. Sometimes the ball rotates in excess of 4000 RPM The inertia of the rotating parts on the head of earlier robots negates their capacity to closely simulate the practice between two players, since reversal of wheel rotation and hence spin, requires too much time.
This invention overcomes the limitation of being unable to reverse the spin on balls successively projected by a single-head robot, when the rate of succession is less than one second. This is possible because in this invention, the ball is ejected by a single rotating wheel which does not impart any required spin to the ball. Spin is developed by separate motors and wheels which are low in mass and are therefore inherently low in inertia. Spin is therefore independent of the speed at which a ball is ejected and can be rapidly reversed without affecting such speed. The result is a table tennis ball projecting mechanism which simulates practice with a human opponent more closely than earlier devices could.
Prior Art to which this invention is related are; (1) U.S. Pat. No. 4,086,903 by Jack C. Scott (2) U.S. Pat. No. 4,325,351 by Yuasa (3) U.S. Pat. No. 3,913,552 by Yarur et al (4) U.S. Pat. No. 3,777,732 by Halloway et al (5) U.S. Pat. No. 3,794,011 by Newgarden (6) U.S. Pat. No. 4,559,918 by Ballerin et at.